The present invention provides for, in some embodiments, hydration acceleration surfactants utilized in conjunction with polymer emulsions, and methods and compositions relating thereto.
High viscosity aqueous-based treatment fluids, e.g., are commonly used in the oil industry in treating subterranean wells, e.g., in fracturing operations, acidizing operations, water control operations, and completion operations. Commonly, such treatment fluids are produced by incorporating into an aqueous-based treatment fluid additives like polymers and, optionally, crosslinking agents (i.e., agents that crosslink the polymer and can further increase the viscosity of the treatment fluid). After addition to the treatment fluid, the polymers and crosslinking agents hydrate, thereby causing the viscosity of the treatment fluid to increase and making reactive sites accessible on each additive.
Lower molecular weight polymers have been used in conjunction with these treatment fluids because they hydrate and form substantially homogeneous mixtures relatively quickly, which consequently makes low molecular weight polymers easy to implement at the well site. However, to create a high viscosity fluid using low molecular weight polymer, a significant loading of polymer is often required, thereby adding significant cost and logistical issues to an operation, especially for remote and offshore well sites. High molecular weight polymers, on the other hand, enable high viscosity fluids at a relatively low polymer loading.
Aqueous-based treatment fluids containing dissolved polymers may be prepared in several ways. Solid polymers may be added to an aqueous base fluid with agitation. Homogeneous solutions can be prepared rapidly when the molecular weight of the polymer is relatively low. However, for high molecular weight polymers, mixing solid polymers with water may take relatively long periods to dissolve even with agitation. Frequently such high molecular weight polymer dissolution efforts suffer from the formation of “fish eyes,” which form, at least in part, because the initial contact between the polymer and the water rapidly hydrates the outer layer of polymer and creates a sticky, rubbery exterior layer that delays or prevents hydration of the interior polymer. This causes the effective concentration of the high molecular weight polymer to be lower, thereby increasing the amount of high molecular weight polymer needed to achieve a desired viscosity.
Alternatively, pre-dissolved aqueous polymer concentrates can be used to produce high-viscosity aqueous-based treatment fluids. Dissolution by this method can be relatively quick. However, the high concentration of polymer required to yield a viable aqueous polymer concentrate lends itself to low molecular weight polymer because high molecular weight polymers yield aqueous polymer concentrates with very high and impractical viscosities, even at low concentrations.
Yet another avenue utilized for incorporating polymer into treatment fluids includes the use of polymer emulsions, which are prepared by emulsion polymerization of the monomers in a non-aqueous continuous phase. This is accomplished by emulsifying aqueous solutions of the monomers in a non-miscible continuous phase such as mineral oil containing suitable emulsifiers followed by polymerization to reach high molecular weights. Using this method, liquid additives containing stable, inverse emulsions with polymer loadings of 20-60% by weight of the internal phase can be produced. The surfactant package used in the production of polymeric emulsions can be designed in such a way that the emulsion can be added directly to aqueous-based treatment fluids to obtain aqueous hydrated polymer solutions. Generally, it is believed that the polymeric emulsions break and the high molecular weight polymers are exposed to and hydrated by the aqueous-based treatment fluids. However, these methods have inherent problems stemming from the need for the high molecular weight polymer to be properly hydrated. For example, the preparation times can be long, and the effective concentration of the polymer in the treatment fluid can be less, which may lead to premature crosslinking.
To ensure proper hydration, treatment fluids that utilize high molecular weight polymers are often mixed in batches and allowed to hydrate for long periods of time before use, e.g., over 24 hours. Accordingly, large volumes of treatment fluids are often mixed well in advance and stored on site until use, which provides for logistical issues and the potential for wasting significant amounts of costly unused treatment fluid that is not needed.
Further, lower effective concentrations of polymer can affect the timing of the crosslinking. That is, the crosslinker is, in effect, at a higher concentration than desired, which translates to premature crosslinking that further increases the viscosity of the treatment. If premature crosslinking occurs before the fluid has reached its desired location within the wellbore and/or subterranean formation, in some instances, the treatment fluid can become unpumpable, thereby causing costly and time-consuming remedial operations to be performed.
Methods and compositions that enable faster hydration of high molecular weight polymers would be of value, in that, they may enable continuous treatment fluid production.